The objectives of the proposed research are to identify and characterize the primary neuronal components involved in mediating both analgesia and tolerance. The specific objectives are to: (1) Determine the developmental onset of the responses of fetal guinea-pig small intestine to opiates. This will be compared to the appearance in ontogeny of the serotonergic, adrenergic, and non-adrenergic inhibitory innervations as well as responses to cyclic AMP. (2) Compare the onset of the physiological responses to morphine with the time course for the development of stereospecific binding of morphine to intestinal opiate receptors. (3) Determine the developmental stage at which fetal intestine can exhibit tolerance to opiates. (4) The effects of chronic exposure to morphine during pregnancy on fetal neuronal development will be examined. (5) Determine if opiate receptors are located in intrinsic or extrinsic components of the myenteric plexus using organotypic tissue culture. (6) Characterize the effects of morphine, serotonin, norepinephrine and phosphodiesterase inhibitors, alone and in combination, on the electrically induced release of acetylcholine from the adult ileum and compare with similar effects on fetal intestine. (7) Determine the effects on analgesia produced when the above combinations of drugs are injected directly into various regions of the brain. (8) Determine the possible involvement of cAMP in mediating the effects of morphine on acetylcholine release. (9) Determine the cellular and subcellular distribution of morphine-like compound (MLC) by immunofluorescence. The project will involve a multi-disciplinary approach using histology, organotypic issue culture, immunofluorescence, biochemistry and physiology.